The present invention relates to printers and in particular digital inkjet printers for wide format printing.
Wide format pagewidth printers are well known with various models commercially available, for example, the HP 3500CP printer from Hewlett-Packard.
Unfortunately, this printer and other similar wide format printers are excessively slow as the printhead prints in a series of transverse swathes across the page.
To overcome this, there have been attempts to design printers that can print the entire width of the page simultaneously. A pagewidth printhead does not traverse back and forth across the page and thereby significantly increases printing speeds. However, proposals for a pagewidth printhead assembly have not become commercially successful because of the functional limitations imposed by standard printhead technology. A 600 dpi thermal bubble jet printhead configured to extend the entire width of a 54 inch wide standard roll of paper would require 136,000 inkjet nozzles and would generate 24 kilowatts of heat during operation. This is roughly equivalent to the heat produced by 24 domestic bar heaters and would need to be actively cooled using a heat exchange system such as forced air or water cooling. This is impractical for most domestic and commercial environments as the cooling system for the printer would probably require some type of external venting. Without external venting, the room in which the printer is situated is likely to get over heated.
The power consumption problem also influences the size of the printhead required for pagewidth wide format printing. The distance between thermal inkjet nozzles cannot be less than a minimum spacing in case the heat generated to fire ink from one nozzle inadvertently fires the ink from an adjacent nozzle. A similar problem applies to piezo-electric inkjet printheads. The piezo-electric material has a small size change per volt applied; typically about 3xc3x9710xe2x88x926 m per volt. Even if this size change is optimised using a bend actuator mechanism, the physical dimensions of the piezo-electric material required to produce the size change necessary to eject ink from a nozzle will only allow a printhead construction with one nozzle per 1 to 4 mm2.
In light of the low nozzle packing densities permitted by the standard inkjet technologies, the size of the printhead required for full color wide format pagewidth printing becomes impractical.
Another obstacle to the commercial manufacturer of pagewidth printheads is the cost. These printheads are formed using Micro-Electro-Mechanical Systems (MEMS) techniques that are similar to the manufacture of silicon computer chips. In this process, the ink nozzles and ejector mechanisms are formed in a series of etching and deposition procedures on silicon wafers as is the case with other computer chips.
The cost of printhead chips is roughly proportional to the area of the wafer required, however, the cost of the printhead does increase disproportionately with an increasing area of wafer used. This is because manufacturing costs begins to escalate as the chip defect rate also increases with wafer size. Faults will inevitably occur during silicon chip manufacture and some level of attrition is always present because of this. A single chip will render an entire pagewidth printhead chip defective as is the case with regular silicon chip production. However, because the pagewidth chip is larger than regular chips, there is a higher probability that any particular chip will be defective thereby raising the defect rate as a whole in comparison to regular silicon chip production. The problem is further exacerbated when much larger pagewidth chips are manufactured for wide format printing.
According to a first aspect, the present invention provides a pagewidth inkjet printer including:
a printhead assembly having an elongate pagewidth array of inkjet nozzles, chambers and thermal bend actuators formed using MEMS techniques;
the printhead assembly being constructed and arranged such that adequate heat dissipation occurs at equilibrium operating conditions without the use of a forced heat exchanged system.
Preferably, the printhead assembly dissipates the majority of the heat produced during the operation of the inkjet nozzles, chambers and actuators is dissipated by the ink ejected from the nozzles. In a further preferred form, the printhead assembly has a plurality of inkjet printhead modules arranged end to end to form the array, each module having a printhead chip in which the nozzles, chambers and actuators are formed wherein the surface area of the chip required for each nozzle is less than 0.5 mm2. In a particularly preferred form, the surface area of the chip required for each nozzle is less than 0.1 mm2 and may conveniently be less than 0.02 mm2.
According to a second aspect, the present invention provides a pagewidth inkjet printer including:
a printhead assembly having an elongate pagewidth array of inkjet nozzles, chambers and thermal bend actuators formed using MEMS techniques;
wherein the array extends at least 36 inches (914 mm) in length; and, the nozzles, chambers and actuators are formed in one or more printhead chips such that the surface area of the chip required for each nozzle is less than 0.5 mm2.
According to another aspect, the present invention provides a pagewidth inkjet printer including:
a printhead assembly having an elongate pagewidth array of inkjet nozzles, chambers and thermal bend actuators formed using MEMS techniques;
wherein the array extends at least 36 inches (800 mm) in length; and, the printhead assembly has a plurality of inkjet printhead modules arranged end to end to form the array.
In a particularly preferred form, the printhead assembly further includes a plurality of printhead units, each unit having a plurality of the printhead modules mounted thereon such that the printhead units are in turn mounted to the printhead assembly to form the array. In some embodiments, 70 printhead modules are abutted in an overlapping format to provide a printhead assembly extending 54 inches (1372 mm). It will be appreciated that by overlapping adjacent printhead modules, the printing produced by each module can be electronically adjusted to precisely abut the printing from modules on either side.
It will be appreciated that by mounting a number of printhead modules on a printhead unit and then using a number of printhead units to form the printhead assembly, there are two levels of modularity in the design which permit defective components to be removed and replaced conveniently and relatively inexpensively.
It has been found that pagewidth printers incorporating printhead chips using thermal bend actuators can produce a high resolution print while consuming significantly less power. A 54 inch wide format pagewidth printhead formed in accordance with standard thermal inkjet technology would provide 136,000 inkjet nozzles to produce a resolution of 600 dpi. It could print 150 foot long roll of standard 54 inch wide paper in approximately 2.4 minutes, however, it will require 24 kilowatts of power of which approximately 20 kilowatts would need to be dissipated by forced air, water or other coolant.
A printer according to the present invention would also print the standard 150 foot length of a 54 inch wide roll in 2.4 minutes, however by using 364,000 nozzles it provides 1600 dpi resolution (generally accepted as photographic quality) and would consume only 0.655 kilowatts which would not require any additional cooling. With this level of power consumption, the ejection of ink would dissipate sufficient heat. This allows a greater nozzle packing density and reduces the overall size of the printhead assembly.